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Diode junction cap equation (Read 4106 times)
ranjang
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Diode junction cap equation
Sep 09th, 2014, 2:51am
 
module diode (a, c);
inout a, c;
electrical a, c;
branch (a, c) i_diode, junc_cap;
parameter real is = 1e-14, tf = 0, cjo = 0, imax = 1, phi = 0.7;
analog begin
I(i_diode) <+ is*(limexp(V(i_diode)/$vt) – 1);
I(junc_cap) <+
ddt(tf*I(i_diode) - 2*cjo*sqrt(phi*(phi*V(junc_cap))));
if (I(<a>) > imax)
$strobe( "Warning: diode is melting!" );
end
endmodule


In this what does the below equation signifies and how it can be derived
I(junc_cap) <+
ddt(tf*I(i_diode) - 2*cjo*sqrt(phi*(phi*V(junc_cap))));

Thanks
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Ken Kundert
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Re: Diode junction cap equation
Reply #1 - Sep 9th, 2014, 10:29am
 
It is the junction capacitance. You can derive it by taking the normal junction capacitance formula for C(v), which equals dq(v)/dv, integrating it with respect to v to get q(v), then applying the time derivative to q(v(t)) to get i(t).

-Ken
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ranjang
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Re: Diode junction cap equation
Reply #2 - Sep 10th, 2014, 5:16am
 
Thanks Ken.
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Geoffrey_Coram
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Re: Diode junction cap equation
Reply #3 - Sep 23rd, 2014, 2:16pm
 
Note that tf*I(i_diode) is a diffusion capacitance; the rest is the usual junction (depletion) capacitance.
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